Pole piece and collector assembly for high frequency electron discharge device with cooling ribs



Dec. 20, 1966 E. G. GRE E L 9 93,430

POLE PIECE AND COLLECTOR AS BL OR HIGH FREQU Y ELECTRON DISCHARGE DEVICE WITH COOLING RIBS 963 2 Sheets-Sheet 1 Filed May 24, l

INVENTORS ELDEN G. GREEN 1: LOUIS T. ZITELLI ATTORNEY 3,293,480 UENCY Dec. 20, 1966 E. G. GREEN ETAL POLE PIECE AND COLLECTOR ASSEMBLY FOR HIGH FREQ ELECTRON DISCHARGE DEVICE WITH COOLING RIBS Filed May 24, 1963 v 2 Sheets-Sheet 2 PRIOR ART INVENTORS ELDEN G. GREEN LOUIS T. ZITELLI United States Patent 3,293,480 POLE PIECE AND COLLECTQR ASSEMBLY FGR HIGH FREQUENCY ELECTRGN DISCHARGE DE- VICE VVETH CGULING REES Elden G. Green and Louis Thomas Zitelli, Palo Alto, Calif., assignors to Varian Associates, Palo Alto, Califi, a corporation of California Filed May 24, 1963, Ser. No. 282,991 7 Claims. (Cl. 315-5.38)

This invention i concerned in general with high frequency electron discharge devices such as, for example, klystrons and traveling wave tubes and more particularly with high power electron beam collectors and heat dissipators therefor.

Electron beam collectors and heat dissipators for CW. and pulsed electron discharge devices such as, for example, high power klystrons used in mobile communication systems and in steerable radar antennas as well as for drivers of larger super power tubes are subject to diverse design constraints. For example, certain of these design considerations include attempts to maximize heat dissipation while minimizing overall weight of the cooling apparatus including weight of the cooling and coolant fluid (liquid or gaseous state) pumping apparatus while simultaneously limiting overall collector volume and weight. When the above requirements are coupled with the requirements of ruggedness and mechanical rigidity, the designer is faced with an imposing array of problems.

A typical prior art beam collector and heat dissipator structure for klystrons which attempts to minimize overall weight of the collector and heat dissipative structure was of the multiple fin forced air cooled type and employed an array of spaced radial directed fins mounted on a tubular main body collector. This collector is limited by the fact that the spacing between adjacent fins increases a the radial distance along the fins from the tubular collector core increases thus resulting in inefiicient cooling for forced air systems and poor mechanical stability as well as limited overall fin cooling surface for a given outer diameter.

Furthermore, this prior art type collector was generally mounted on the tube proper and insulated therefrom by means of a ceramic insulating ring located at or near the end wall of the output cavity in the case of a klystron. This, of course, resulted in the subjection of the ceramic ring and accompanying metal joints to severe thermal stresses which under high power operating conditions could easily result in cracking of the ceramic and accompanying joints,

An additional problem is encountered when the insulating ceramic ring is displaced from the end wall position, namely, that of weight distribution of the collector structure on the ceramic ring and means for assuring positive D.C. isolation of the collector from the tube main body during operation under adverse thermal and vibratory conditions of operation.

The present invention besides resulting in a far more efficient cooling apparatus than the above-mentioned radial type also prOVides unique means for supporting the collector core and fin structure within a cup-shaped pole piece member and insulating said structure from the cupshaped pole piece member as well as the remainder of the tube proper in such a manner that mechanical and heat stresses on a weight bearing ceramic ring-member are minimized. This is accomplished by locating the ceramic ring insulator which both insulates and supports the collector structure with respect to the tube proper in a transverse plane passing through the collector center of gravity or as near thereto as possible. This arrangement eliminates the problems encountered in providing ceramic to metal seals at points of extreme temperature such as are found at the juncture of the output cavity and collector proper wherein dilferential thermal expansion problems between metal and ceramic materials render joints at such locations quite susceptible to cracking at high operating temperatures. Location of the ceramic insulator support ring in a transverse plane through, or as near as possible thereto, the center of gravity of the collector structure also minimizes mechanical stresses on this member which would become quite pronounced when such a collector structure is utilized in, for example, an electron discharge device such as a high power klystron tube mounted on a steerable antenna or other mobile type of equipment wherein the tube is subjected to acceleration stresses. Additional collector stabilizing insulating balls are positioned in spaced recesses located in the exterior surface of the collector core in order to minimize stresses on the abovementioned ceramic insulator support ring due to acceleration stresses while simultaneously preventing any possible shorting from occurring between the collector structure and the tube main body.

It is therefore an object of the present invention to provide a novel electron beam dissipation structure for high frequency electron discharge devices such as klystrons and traveling wave tubes and the like.

Another feature of the present invention is the provision of -a high frequency electron discharge device having an insulated collector structure wherein said collector structure is supported by an insulating ring located substantially near or on a transverse plane th-rought he center of gravity of the collector structure.

Another feature of the present invention is the provision of a plurality of spaced stabilizing members located on the exterior surface of the collector core which opposes the inner surface of the cup-shaped pole piece in order to insure electrical isolation between the collector structure and the tube main body While simultaneously preventing undue stresses due to gravitational or acceleration forces from cracking the insulating ring.

Another feature of the present invention lies in the combination of the two directly preceding features.

These and other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in conjunction with the accompanying drawings wherein,

FIG. 1 is a longitudinal view partially sectioned and partially in elevation of a high frequency and high power multicavity klystron amplifier incorporating the novel collector structure of the present invention,

FIG. 2 is a reduced transverse cross-sectional view taken along the lines 22 of FIG. 1 showing the stabilizing insulator balls incorporated in spaced slots inthe exterior surface of the collector core,

FIG. 3 is an enlarged partial cross-sectional view taken along the lines 33 of FIG. 1 showing the general curvature and arrangement of the cooling fins mounted on the collector core,

FIG. 4 is a descriptive geometric portrayal of the curvature and length of a single cooling fin of the present invention,

FIG. 5 is a geometric representation of a typical radial fin prior art collector stnicture,

FIG. 6 is a geometric representation of the novel fin geometry of the present invention embodied in a collector configuration which more or less typifies the universal exterior and interior configurations to which the novel fin geometry may be applied,

FIG. 7 is a geometric representation of a modified cooling arrangement employing the novel fin geometry of the present invention, and

FIG. 8 is a geometric representation of another fin geometry wherein arcs of ellipsoids are employed.

Referring now to FIG. 1 there is depicted therein a high frequency C.W. multicavity klystron amplifier 1, incorporating the novel collector structure 2, of the present invention. The electron gun end 14, of the tube utilizes conventional annular ceramic 3 and Kovar 4 housing members within which the cathode structure is mounted. The electron beam emanating from the cathode is preferably a solid pencil shaped beam which is initially focused by focusing electrode 5 after which the beam traverses in sequence anode 6, drift tube '7, interaction gap 8, drift tube 9, etc., to the output cavity 10. The electron beam then terminates past the pole piece 11 of the cup-shaped collector pole piece and support member 12 into the central aperture within collector core member 13 whereupon normal space charge effects cause beam dispersion and resultant power dissipation in the collector structure in the form of heating of the collector structure 2.

The tube main body section 15 is preferably of OFHC copper and has a plurality of cavity sections as shown each individually tunable by means of tuning structures 16, each of which contains a spring loaded plunger 17 bearing on a cavity tuner diaphragm 18 as shown, for example, with reference to output cavity 10. The main tube body itself is provided with a plurality of cooling fins 19 preferably of copper to aid in dissipating heat from the tube main body.

Conventional input and output waveguides 2t), 21 having vacuum tight waveguide window sections 22, 23 are used to couple R.F. energy into and out of the input and output cavities of the tube.

Turning our attention to the collector structure 2, the present invention incorporates a cup-shaped collector pole piece 12 preferably of a magneti material such as cold rolled steel having internal flange members 11 functioning as a magnetic pole for the collector end of the tube. A permanent magnet focusing structure (not shown) similar to that shown and described in US. Patent Ser. No. 2,915,670, by Louis T. Zitelli, one of the co-inventors of the subject application, is preferably employed in a C.W. klystron of the type shown in FIG. 1. The pole piece flange 11 is preferably brazed to the end wall 24 of tube main body 15.

Collector core 13, preferably of copper material, is supported within the cup-shaped collector pole piece 12 by means of overlapping internal and external flanged ring members 26, 27, respectively, which are preferably of Kovar. Internal ring-shaped member 26 is preferably brazed on one end portion thereof to a cold rolled steel annulus 28 which in turn is brazed to the external peripheral surface of the collector core 13 as shown while external ring-shaped member 27 is preferably brazed on the one end thereof to stepped portion of the cup-shaped pole piece member 12 as shown. Sandwiched between and brazed to the external flanged portions 29, 30 of ringshaped members 26, 27 is an annular ceramic support ring 31 made from a material such as, for example, commercially available AL300 which functions both as a support means in conjunction with members 26, 27 for the collector core 13 and as a vacuum joint for the tube proper. A conventional fly trap member 32 preferably of OFHC copper is fixedly mounted within a stepped beam entrance portion of the collector core 13, as shown, by means of any suitable metal joining technique.

Insulating balls 33 preferably of alumina are positioned within spaced cubic-shaped bores in the collector core 13 as best seen in FIG. 2. The diameter of the balls is slightly smaller than the width or length of the bores so that the balls may be easily positioned therein and retained therein by means of a swaging tool which deforms the outer edges of the bore. A clearance of approximately /a inch is left between the external diameter of core 13 and the internal diameter of cup-shaped pole piece member 12 whereas a clearance of approximately 0.025 inch is left between the interior surface of cup-shaped pole piece member 12 and the nearest opposing surface portion of the insulating balls. This relatively minute clearance permits the collector core to be easily slipped within the open end of the member 12 and forms a dual function of assuring continuous insulation of core 13 from member 12 regardless of external forces such as those due to acceleration or gravitational stresses acting on the tube. Such external forces would otherwise produce sufficient deflection of the core 13 to cause shorting between core 13 and the cup-shaped pole structure 12. In addition the balls 33 prevents any excessive forces from occurring between the core 13 and member 12 from cracking or breaking the support ring 31 and/ or the seals between ring 31 and the ring-shaped members 26, 27. This second function is accomplished by virtue of the minute spacing left between the insulating balls and the internal surface of member 12 which eliminates the possibility of pendulum or oscillatory motion type stresses from building up between core 13 and member 12 to such an extent that a fracture of the ring insulator 31 or any of its sealed joints will occur. The number of balls may vary from as few as three equally spaced balls to any greater number.

The location of the insulator ring 31 is advantageously positioned in a transverse plane through the center of gravity of the collector structure 2 which comprises core 13 and fins 35. This serves the function of removing the insulator joint between the collector structure and the tube body from a location of high operating temperature such as occurs at the juncture of the collector cup-shaped pole piece member 12 and the end wall 24 of output cavity 10 of the tube to a point of relatively low operating temperature and thus minimizing stresses due to diflerential thermal expansion between materials of dissimilar temperature coefficients of expansion. Furthermore, the location of the insulating ring 31 in a transverse plane near or at the center of gravity of the collector structure results in an equal weight distribution on the ring itself as well as lessening the possibility of pendulum or oscillatory type stresses from possibly fracturing the ring or its joints.

As best seen in FIG. 3, the present invention incorporates a novel arrangement of the collector cooling fins 35. FIG. 5 shows a typical prior art type collector cooling fin arrangement wherein a plurality of radial fins 38 are mounted on and radially directed from core 39 as shown. It is readily apparent that this design suifers from various defects such as unequal spacing D between adjacent fins along the radial extent S, of the fins. This, of course, results in uneven cooling of the fins since the highest fluid velocity occurs .at the outermost portion of the fins where the spacing between adjacent fins is greatest which, of course, results in the highest rate of cooling at the point where the fin temperature is lowest and thus is a relatively ineflicient way of cooling. Furthermore, the total fin surface available for cooling is, of course, limited by the total number, thickness of .and spacing between fins and by the chosen outer diameter. In the case such as depicted in FIG. 5, this total fin area is relatively limited.

A further defect of the cooling fin arrangement of FIG. 5 lies in the fact that a relatively structurally weak fin which is unsupported at the outermost radial end portion is the end result. Furthermore, the mechanical resonant frequencies of such a fin geometry as depicted in FIG. 5 are relatively low and thus are more easily induced in a typical mobile environment wherein oscillatory motion is encountered than would be a fin geometry having higher mechanical resonant frequencies than the radial fins of FIG. 5. This structural weakness can, of course, be obviated to a certain degree by the addition of an exterior cylindrical member such as 40. However, this presents metal joining problems because of the rather inaccessible location of the surfaces to be joined.

The collector fin of the instant invention obviates all of these above-mentioned cooling and structural defects by utilizing a novel curved fin geometry. I

The maximum fin surface area for a given fin thickness, given spacing between adjacent fins, at the interior base of the fins and a given outer diameter occurs for a finhaving a geometry which maintains equal perpendicular spacing D between adjacent fins at all opposing points of the fin surfaces.

Such a fin geometry has the following advantages over the radial fins of FIG. 5. For a given volume of air flow in. aforced air cooling system, the surface velocity of the cooling air will remain substantially constant over the entire fin surface. This results in substantially maximum heat transfer efiiciency from the fin surface to the air for a given air velocity. Furthermore, the curved geometry of the cooling fins 35 of FIG. 3 are mechanically more stable than the radial fins of FIG. 5 since the mechanical resonant frequencies of the curved geometry are much higher than the resonances of radial fins. Additionally the fins of the present invention can be punched and shaped with ease from copper sheet stock with a minimum of effort and brazed in longitudinal slots 36 extending along the axial direction of the core 13 with a minimal effort and each fin is advantageously shaped with a bent end portion 42 which is brazed as shown at 37 to each adjacent fin along the axial extent of the fins with the resultant eflFect of creating an extremely rugged collector cooling section without the necessity of providing an additional outer annular member such as 40 of FIG. 5 with the metal joining problems inherent in such a design.

The curvature of a fin of the present invention can be mathematically defined as the involute of a circle for the perfect case of maximum fin surface area for a given exterior diameter, a given fin spacing at the interior base of the fins and a given fin thickness.

The equation is given by 0= /P 1arc cos l/P where P= and P To 7'0 wherein r, r r 0 and S are defined by reference to FIG. 4.

The transverse length of the fin S is related to r and r as follows:

8 2 To m 1 Taking a typical case for the fin geometry of FIG. 4 where In the case of the fin geometry shown in FIG. 5, the transverse or radial fin length S would be therefore, for this particular case, the curved fin geometry would develop 1.5 times more area than the conventional flat fin.

It is to be understood that the geometric configurations surrounding the fin geometry of the present invention are not limited to concentric cylinders such as depicted in FIGS. 3 and 4. The curved fin geometry of the pres-ent invention can equally advantageously be employed in such diverse geometries as coaxial squares, coaxial rectangles, coaxial square and circle, coaxial circle and square, etc. The universal applicability of the unique fin geometry of the present invention is clearly shown in FIG. 6 wherein more or less arbitrary interior and exterior geometries are utilized with the fin geometry of the present invention. Furthermore the geometry of the present invention is easily applicable to tube main body portions as well as collector structures.

FIG. 7 depicts a modified embodiment-of the unique fin geometry wherein alternate concentric cylinders defined by the curved fin geometry of the present invention are shown where adjacent fin sections such as 45, 46, 47, 48 have reversed curvatures. Each section maintains constant spacing between fins as in the embodiment of FIG. 3 and has all thermal and mechanical properties of the structure of FIG. 3. Again as in the embodiment of FIG. 3 simple machining and shaping (stamping) operations may be advantageously employed to construct the fins of FIG. 7. Also as in FIG. 3 the end portions 49 of each fin of FIG. 7 are advantageously bent and joined to the adjacent fin to greatly increase the overall ruggedness of the structure. A simple way of defining the structure of FIG. 7 would be to refer to each concentric fin section 45, 46, etc, as being generated :from a radius r moving in a clockwise or a counterclockwise direction about the center of a circle. The individual fins of the embodiment of FIG. 7 are advantageously stamped from a single sheet of material such as, for example, copper.

It is further to be noted that the present invention is not limited to the involute geometry for the fins and it is contemplated that other fin configurations which give variable spacing between the interior and exterior, core and outer boundary, respectively, can equally advantageouslybe employed and are easily derived by one skilled in the art after a perusal of the instant specification. For example, ordinary arcs of circles or other curved surfaces such as elliptical fin geometries can be mounted on a core and by suitably selecting a sufficient number thereof it is obvious that the core will be surrounded in the same manner as shown in FIGS. 1 and 3, for example, differing therefrom only in the fin geometry and spacing therebetween and total number of fins surrounding the core. An extremely strong structure results as in the case of the involute when the fin end portions are bent to engage and are bounded to the adjacent fins as in FIGS. 1 and 3 and all the manufacturing advantages of FIGS. 1 and 3 remain. An example of another geometry other than the involute is shown in FIG. 8 wherein a plurality of generally elliptical shaped fins 55 having bent ends 56 surrounding core 57.

Cooling fins having the geometry of FIGS. 3 and 4 have been constructed with a fin thickness of .040 in., fin perpendicular spacing D of .075 in., axial interior length of 3% in., flattened width of 1.465 in., axial exterior length of 3% in. Sixty four copper fins of the above dimensions were positioned in sixty-four parallel axially directed grooves 36, in an OFHC copper collector core having a 1 in. interior diameter and a 2.125 in. outer diameter and easily dissipated 5.0 kw. with a forced air cooling flow of cfm. at 1.5 in. of water and 25 C. air inlet temperature. The above design could easily be adapted utilizing the above design criteria to handle considerably higher kw. of power.

Since many changes could be made in the above construction and many apparently widely different embodiments of this inventioin could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. What is claimed is: 1. A collector structure for a high frequency electron discharge device comprising,

a cup-shaped pole piece member of magnetic materia a thermally conductive collector core member disposed within and in DC. isolation with said cup-shaped pole piece member,

said core member being supported on and mechanically attached to said pole piece member by means of an insulating support ring, said ring being located in a transverse plane, said transverse plane traversing approximately through the center of gravity of said core member, said device further including a plurality of insulating members positioned near one end of said core member, said one end being disposed within said pole piece member, said plurality of insulating members being disposed relative to said core member and said pole piece member such that DO electrical shorting between said core member and said pole piece member cannot occur due to relative displacement forces occurring between said core member and said pole piece member.

2, The structure as defined in claim 1 wherein said plurality of insulating members is larger than two and wherein said insulating members are generally spherical shaped and wherein said spherical shaped members are disposed in a plurality of spaced holes located in the exterior surface portion of said core member, said spherical shaped members having a diameter which is slightly larger than the depth of said holes.

3. The structure as defined in claim 1 and further comprising a plurality of cooling fins fixedly mounted on said core member, said cooling fins having .a curved geometry.

4. The structure as defined in claim 3 wherein said cooling fins have a geometry which is equivalent to the involute of a circle whereby approximately equal perpendicular spacing between adjacent fins is maintained along the transverse length of said fins.

5. The structure as defined in claim 3 wherein said said first section of cooling fins comprising a plurality of cooling fins each of which has a curved geometry, said geometry being such that equal spacing between adjacent fins is maintained over the transverse length of the fins, said fins of said first section having .a clockwise orfentation about said central axis, a second section of cooling fins mounted around said electron discharge device, said second section of cooling fins comprising a plurality of cooling fins each of which has a curved geometry, said geometry being such that equal spacing between adjacent fins is maintained over the transverse length of the fins, said fins of said second section having a counterclockwise orientation about said central axis, said fins of said first and said second sections being constructed from a single metal member.

7. A high frequency electron discharge device including a cup-shaped pole piece member of magnetic material thermally conductive collector core member having .a portion thereof disposed within and in DC. isolation with respect to said cup-shaped pole piece member, said core member being supported on and mechanically attached to said pole piece member by means of an insulating support ring, said core member and said cup-shaped pole piece member having plural insulating means disposed therebetween at the end portion of said core member which is disposed within said cup-shaped pole piece member.

References Cited by the Examiner UNITED STATES PATENTS 2,687,490 8/1954 Rich et al 3l55.34

FOREIGN PATENTS 63,252 3/1955 France.

785,065 10/1957 Great Britain.

JAMES W. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistant Examiner. 

1. A COLLECTOR STRUCTURE FOR A HIGH FREQUENCY ELECTRON DISCHARGE DEVICE COMPRISING, A CUP-SHAPED POLE PIECE MEMBER OF MAGNETIC MATERIAL, A THERMALLY CONDUCTIVE COLLECTOR CORE MEMBER DISPOSED WITHIN AND IN D.C. ISOLATION WITH SAID CUP-SHAPED POLE PIECE MEMBER, SAID CORE MEMBER BEING SUPPORTED ON AND MECHANICALLY ATTACHED TO SAID POLE PIECE NUMBER BY MEANS OF AN INSULATING SUPPORT RING, SAID RING BEING LOCATED IN A TRANSVERSE PLANE, SAID TRANSVERSE PLANE TRAVERSING APPROXIMATELY THROUGH THE CENTER OF GRAVITY OF SAID CORE MEMBER, SAID DEVICE FURTHER INCLUDING A PLURALITY OF INSULATING MEMBERS POSITIONED NEAR ONE END OF SAID CORE MEMBER, SAID ONE END BEING DISPOSED WITHIN SAID POLE PIECE MEMBER, SAID PLURALITY OF INSULATING MEMBERS BEING DISPOSED RELATIVE TO SAID CORE MEMBER AND SAID POLE PIECE MEMBER SUCH THAT D.C. ELECTRICAL SHORTING BETWEEN SAID CORE MEMEBR AND SAID POLE PIECE MEMBER CANNOT OCCUR DUE TO RELATIVE DISPLACEMENT FORCES OCCURRING BETWEEN SAID CORE MEMBER AND SAID POLE PIECE MEMBER. 